Output power meter



May 31, 1938. s rrH, JR 2,119,364

OUTPUT POWER METER Filed Aug. 28, 1937 7 Wi 1 6R.

A ORNEYS.

Patented May 31,1938 1 2,119,364

UNITEDSTATES PATENT OFFICE OUTPUT POWER METER John P. Smith, Jr., Ridgewood, N. J., assignor to The Daven Company, Newark, N. J., a corporation of New Jersey Application August 28, 1937, Serial No. 161,503

3 Claims. (Cl. 17195) This invention relates to output power meters rheostat has also the advantage of being able and has for an object a practical and inexpensafely to dissipate higher energy values than a sive power meter which has a high degree of actransformer without the inherent ill-effects of curacy both for frequency and impedance charoverloading of the transformer. Such a power acteristics. output meter effects a reduction in frequency er- 5 Output power meters, although fairly new in ror to approximately 5% over the entire range the industry, have a widespread application. from 20 to 10,000 cycles and a reduction in the They are capable of measuring the power output impedance error to 5% for the same frequency of a generator source such as an amplifier or osrange.

cillator by providing a large selection of terminat- Other objects, novel features and advantages of 10 ing impedances for such source and measuring this invention will become apparent from the the voltage which is developed across such terfollowing specification .and accompanying drawmination. With the indicating meter calibrated ing, wherein the single figure illustrates a cirto read in milliwatts, it is possible to use this cuit embodying the invention.

instrument as a very rapid means of determining An alternating current volt meter II] prefer- 15 the power delivered by any given generator ably of 5000 ohms impedance is connected in cirsource to any desired load, of determining the cult with the terminal binding posts ll, l2 to impedance value of an unknown load, of deterwhich may be connected the generator source to mining the proper impedance value of the load be tested. A variable resistance [3 is connected for maximum transfer of energy, of determining in series with the meter Ill and a variable re- 20 the impedance versus frequency characteristics sistance I4 is connected in shunt with the resistof the generator source and/or with the connectance to form a variable L attenuator. A rheostat ing transmission line, of determining the iml5 and a variable auto transformer I6 are bridged pedance versus frequency characteristics of the across said L attenuator. The rheostat I5 is proexisting load and of determining the proper imvided with contacts I! and contacts l8 are tapped 25 pedance value for a mismatched load when such to the auto transformer IS. A sliding contact [9 circumstances are desirable. has arms engaging the contacts I! and [8 so that Heretofore, output power meters have been the rheostat and auto transformer are simultabased on the use of tapped transformers for the neously controlled.

major control device. However, the use of a In operation, the rheostat I 5 terminates the 30 variable transformer as a load determination ingenerator source under test and provides the troduces a frequency error, corrections for which desired range of terminations which in standard must be applied to the extent of 25% for readinstruments is from 2.5 to 20,000 ohms. The ings outside of the band of 150 to 2,500 cycles. bridging transformer 16 has a ten to one bridging a For most purposes, this frequency band is enratio which is too high with respect to the rheotirely too limited at the present stage of the art. statto have any noticeable effect upon the load Furthermore, such arrangement introduces ertermination or upon the generator source. This rors in impedance measurements as great as 7% transformer functions to step up the V t in the frequency range from 150 to- 3,000 cycles which is developed across that portion of the and as high as when the instrument is used rheostat used as the load. From this point on, 40 for measurements from 20 170 10,000 Cy es. In the instrument is essentially a high impedance addition. a t a s Of this yp is expensive A. C. volt meter except that the meter and its to manufacture, even for such llmited accuracy associated controls are calibrated to read directly and its cost would increase rapidly for any slight in mmiwatts and/or decibe1s 45 Improvement in accuracy The above-described meter is of materially 45 In an output power meter embodying mhe higher accuracy both for frequency and impedpresent invention, a rheostat is used as the teranc r c 1 1c 1 h ll'l n mmatmg element and a variable auto transe aha ter St S W t out be g y more ex former is used as a bridging device, means being penslve thajn prevlous power The 5 provided for simultaneously controlling the rheomovement m P great y mcrea ses the 0 t t and t tran fo men The use of a fulness of the instrument as it may be used m sistance terminating element eliminates considlaboratories to replace a elaborate D erable difficulties due to phase relations as well VOlVing several u e ts to Obtain the same as the frequency and impedance errors experinction.

enced with the transformer termination. The I claim: 55

10 the terminals of said auto transformer, and variable resistances in series with and in shunt to said volt meter.

3. A device of the character described comprising a rheostat and a variable auto transformer in parallel, a volt meter connected across the terminals of said auto transformer, variable resistances in series with and in shunt to said volt meter, and means for simultaneously controlling said rheostat and said auto transformer.

JOHN P. SMITH, JR. 

